Inbred corn line PHRD6

ABSTRACT

According to the invention, there is provided an inbred corn line, designated PHRD6. This invention thus relates to the plants and seeds of inbred corn line PHRD6 and to methods for producing a corn plant produced by crossing the inbred line PHRD6 with itself or with another corn plant. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line PHRD6 with another corn line or plant.

FIELD OF THE INVENTION

This invention is in the field of corn breeding, specifically relatingto an inbred corn line designated PHRD6.

BACKGROUND OF THE INVENTION Plant Breeding

Field crops are bred through techniques that take advantage of theplant's method of pollination. A plant is self-pollinated if pollen fromone flower is transferred to the same or another flower of the sameplant. A plant is cross-pollinated if the pollen comes from a flower ona different plant.

Corn plants (Zea mays L.) can be bred by both self-pollination andcross-pollination techniques. Corn has separate male and female flowerson the same plant, located on the tassel and the ear, respectively.Natural pollination occurs in corn when wind blows pollen from thetassels to the silks that protrude from the tops of the incipient ears.

The development of a hybrid corn variety involves three steps: (1) theselection of plants from various germplasm pools; (2) the selfing of theselected plants for several generations to produce a series of inbredlines, which, although different from each other, breed true and arehighly uniform; and (3) crossing the selected inbred lines withunrelated inbred lines to produce the hybrid progeny (F₁). During theinbreeding process in corn, the vigor of the lines decreases. Vigor isrestored when two unrelated inbred lines are crossed to produce thehybrid progeny. An important consequence of the homozygosity andhomogeneity of the inbred lines is that the hybrid resulting from across between any two inbreds will always be the same. Once the inbredsthat produce a superior hybrid have been identified, the hybrid seed canbe reproduced indefinitely as long as the homogeneity of the inbredparents is maintained.

The objective of commercial maize inbred line development programs is todevelop new inbred lines that combine to produce high grain yields andsuperior agronomic performance in hybrid combination. The primary traitbreeders seek is yield. However, other major agronomic traits are ofimportance in hybrid combination and have an impact on yield orotherwise provide superior performance in hybrid combinations. Suchtraits include percent grain moisture at harvest, relative maturity,resistance to stalk breakage, resistance to root lodging, grain quality,and disease and insect resistance. In addition the lines per se musthave acceptable performance for parental traits such as seed yields,kernel sizes, pollen production, all of which affect ability to provideparental lines in sufficient quantity and quality for hybridization.Traits have been shown to be under genetic control and many if not allof the traits are affected by multiple genes. Thus, to be selected as aninbred line, the inbred must be able to combine such that the desiredtraits are passed to the hybrid and also be able to satisfy productionrequirements as a parental line.

Pedigree Breeding

The pedigree method of breeding is the mostly widely used methodologyfor new inbred line development.

In general terms this procedure consists of crossing two inbred lines toproduce the non-segregating F₁ generation, and self pollination of theF₁ generation to produce the F₂ generation that segregates for allfactors for which the inbred parents differ. An example of this processis set forth below. Variations of this generalized pedigree method areused, but all these variations produce a segregating generation whichcontains a range of variation for the traits of interest.

EXAMPLE 1 Hypothetical Example of Pedigree Breeding Program

Consider a cross between two inbred lines that differ for alleles atfive loci. The parental genotypes are:

    ______________________________________                                        Parent 1                                                                             A      b     C   d   e   F/A  b   C   d    e   F                       Parent 2                                                                             a      B     c   D   E   f/a  B   c   D    E   f                       ______________________________________                                    

the F₁ from a cross between these two parents is:

    ______________________________________                                        F.sub.1  A b C d e F/a B c D E f                                              ______________________________________                                    

Selfing F₁ will produce an F₂ generation including the followinggenotypes:

    ______________________________________                                                 A B c D E f/a b C d e F                                                       A B c D e f/a b C d E F                                                       A B c D e f/a b C d e F                                              .                                                                             .                                                                             ______________________________________                                    

The number of genotypes in the F₂ is 3⁶ for six segregating loci (729)and will produce (2⁶)-2 possible new inbreds, (62 for six segregatingloci).

Each inbred parent which is used in breeding crosses represents a uniquecombination of genes, and the combined effects of the genes define theperformance of the inbred and its performance in hybrid combination.There is published evidence (Smith, O. S., J. S. C. Smith, S. L. Bowen,R. A. Tenborg and S. J. Wall, TAG 80:833-840 (1990)) that each of theselines are different and can be uniquely identified on the basis ofgenetically-controlled molecular markers.

It has been shown (Hallauer, Arnel R. and Miranda, J. B. Fo.Quantitative Genetics in Maize Breeding, Iowa State University Press,Ames Iowa (1981)) that most traits of economic value in maize are underthe genetic control of multiple genetic loci, and that there are a largenumber of unique combinations of these genes present in elite maizegermplasm. If not, genetic progress using elite inbred lines would nolonger be possible. Studies by Duvick and Russell (Duvick, D. N. Maydica37:69-79 (1992); Russell, W. A. Maydica XXIX:375-390 (1983)) have shownthat over the last 50 years the rate of genetic progress in commercialhybrids has been between 1 and 2% per year.

The number of genes affecting the trait of primary economic importancein maize, grain yield, has been estimated to be in the range of 10-1000.Inbred lines which are used as parents for breeding crosses differ inthe number and combination of these genes. These factors make the plantbreeder's task more difficult. Compounding this is evidence that no oneline contains the favorable allele at all loci, and that differentalleles have different economic values depending on the geneticbackground and field environment in which the hybrid is grown. Fiftyyears of breeding experience shows that there are many genes affectinggrain yield and each of these has a relatively small effect on thistrait. The effects are small compared to breeders' ability to measuregrain yield differences in evaluation trials. Therefore, the parents ofthe breeding cross must differ at several of these loci so that thegenetic differences in the progeny will be large enough that breederscan develop a line that increases the economic worth of its hybrids overthat of hybrids made with either parent.

If the number of loci segregating in a cross between two inbred lines isn, the number of unique genotypes in the F₂ generation is 3^(n) and thenumber of unique inbred lines from this cross is {(2^(n)) -2}. Only avery limited number of these combinations are useful. Only about 1 in10,000 of the progeny from F₂ 's are commercially useful.

By way of example, if it is assumed that the number of segregating lociin F₂ is somewhere between 20 and 50, and that each parent is fixed forhalf the favorable alleles, it is then possible to calculate approximateprobabilities of finding an inbred that has the favorable allele at{(n/2)+m} loci, where n/2 is the number of favorable alleles in each ofthe parents and m is the number of additional favorable alleles in thenew inbred. See Example 2 below. The number m is assumed to be greaterthan three because each allele has so small an effect that evaluationtechniques are not sensitive enough to detect differences due to threeor less favorable alleles. The probabilities in Example 2 are on theorder of 10⁻⁵ or smaller and they are the probabilities that at leastone genotype with (n/2)+m favorable alleles will exist.

To put this in perspective the number of plants grown on 60 millionacres (approximate US corn acreage) at 25000 plants/acre is 1.5×10¹².

EXAMPLE 2 Probability of Finding an Inbred with m of n Favorable Alleles

Assume each parent has n/2 of the favorable alleles and only 1/2 of thecombinations of loci are economically useful.

    ______________________________________                                        no. of   no. favorable                                                                             no. additional                                                                             Probability                                 segregating                                                                            alleles in  favorable alleles                                                                          that genotype                               loci (n) Parents (n/2)                                                                             in new inbred                                                                              occurs*                                     ______________________________________                                        20       10          14           3 × 10.sup.-5                         24       12          16           2 × 10.sup.-5                         28       14          18           1 × 10.sup.-5                         32       16          20           8 × 10.sup.-6                         36       18          22           5 × 10.sup.-6                         40       20          24           3 × 10.sup.-6                         44       22          26           2 × 10.sup.-6                         48       24          28           1 × 10.sup.-6                         ______________________________________                                         *Probability that a useful combination exists, does not include the           probability of identifying this combination if it does exist.            

The possibility of having a usably high probability of being able toidentify this genotype based on replicated field testing would be mostlikely smaller than this, and is a function of how large a population ofgenotypes is tested and how testing resources are allocated in thetesting program.

At Pioneer Hi-Bred International, a typical corn research station has astaff of four, and 20 acres of breeding nursery. Those researchers plantthose 20 acres with 25,000 nursery rows, 15,000 yield test plots in10-15 yield test sites, and one or two disease-screening nurseries.Employing a temporary crew of 20 to 30 pollinators, the station makesabout 65,000 hand pollinations per growing season. Thus, one of thelargest plant breeding programs in the world does not have asufficiently large breeding population to be able to rely upon "playingthe numbers" to obtain successful research results. Nevertheless,Pioneer's breeders at each station produce from three to ten new inbredswhich are proposed for commercial use each year. At the 32 Pioneerresearch stations in North America, this amounts to from about 100 to300 new inbreds proposed for use with less than 50 and, more commonly,less than 30 of these inbreds eventually satisfying the performancecriteria for commercial use.

This is a result of plant breeders using their skills, experience andintuitive ability to select inbreds having the necessary qualities.

SUMMARY OF THE INVENTION

According to the invention, there is provided a novel inbred corn line,designated PHRD6. This invention thus relates to the seeds of inbredcorn line PHRD6, to the plants of inbred corn line PHRD6, and to methodsfor producing a corn plant produced by crossing the inbred line PHRD6with itself or another corn line. This invention further relates tohybrid corn seeds and plants produced by crossing the inbred line PHRD6with another corn line.

DEFINITIONS

In the description and examples that follow, a number of terms are usedherein. In order to provide a clear and consistent understanding of thespecification and claims, including the scope to be given such terms,the following definitions are provided. ABS is in absolute terms and %MN is percent of the mean for the experiments in which the inbred orhybrid was grown.

BAR PLT=BARREN PLANTS. The percent of plants per plot that were notbarren (lack ears).

BRT STK=BRITTLE STALKS. This is a measure of the stalk breakage near thetime of pollination, and is an indication of whether a hybrid or inbredwould snap or break near the time of flowering under severe winds. Dataare presented as percentage of plants that did not snap.

BU ACR=YIELD (BUSHELS/ACRE). Actual yield of the grain at harvest inbushels per acre adjusted to 15.5% moisture.

DRP EAR=DROPPED EARS. A measure of the number of dropped ears per plotand represents the percentage of plants that did not drop ears prior toharvest.

EAR HT=EAR HEIGHT. The ear height is a measure from the ground to thehighest placed developed ear node attachment and is measured in inches.

EAR SZ=EAR SIZE. A 1 to 9 visual rating of ear size. The higher therating the larger the ear size.

EST CNT=EARLY STAND COUNT. This is a measure of the stand establishmentin the spring and represents the number of plants that emerge on a perplot basis for the inbred or hybrid.

GDU SHD=GDU TO SHED. The number of growing degree units (GDUs) or heatunits required for an inbred line or hybrid to have approximately 50percent of the plants shedding pollen and is measured from the time ofplanting. Growing degree units are calculated by the Barger Method,where the heat units for a 24-hour period are: ##EQU1##

The highest maximum temperature used is 86° F. and the lowest minimumtemperature used is 50° F. For each inbred or hybrid it takes a certainnumber of GDUs to reach various stages of plant development.

GDU SLK=GDU TO SILK. The number of growing degree units required for aninbred line or hybrid to have approximately 50 percent of the plantswith silk emergence from time of planting. Growing degree units arecalculated by the Barger Method as given in GDU SHD definition.

GRN APP=GRAIN APPEARANCE. This is a 1 to 9 rating for the generalappearance of the shelled grain as it is harvested based on such factorsas the color of the harvested grain, any mold on the grain, and anycracked grain. High scores indicate good grain quality.

MST=HARVEST MOISTURE. The moisture is the actual percentage moisture ofthe grain at harvest.

PLT HT=PLANT HEIGHT. This is a measure of the height of the plant fromthe ground to the tip of the tassel in inches.

POL SC=POLLEN SCORE. A 1 to 9 visual rating indicating the amount ofpollen shed. The higher the score the more pollen shed.

POL WT=POLLEN WEIGHT. This is calculated by dry weight of tasselscollected as shedding commences minus dry weight from similar tasselsharvested after shedding is complete.

It should be understood that the inbred can, through routinemanipulation of cytoplasmic factors, be produced in a cytoplasmicmale-sterile form which is otherwise phenotypically identical to themale-fertile form.

PRM=PREDICTED RM. This trait, predicted relative maturity (RM), is basedon the harvest moisture of the grain. The relative maturity rating isbased on a known set of checks and utilizes standard linear regressionanalyses and is referred to as the Comparative Relative Maturity RatingSystem which is similar to the Minnesota Relative Maturity RatingSystem.

RT LDG=ROOT LODGING. Root lodging is the percentage of plants that donot root lodge; plants that lean from the vertical axis at anapproximately 30° angle or greater would be counted as root lodged.

SCT GRN=SCATTER GRAIN. A 1 to 9 visual rating indicating the amount ofscatter grain (lack of pollination or kernel abortion) on the ear. Thehigher the score the less scatter grain.

SDG VGR=SEEDLING VIGOR. This is the visual rating (1 to 9) of the amountof vegetative growth after emergence at the seedling stage(approximately five leaves). A higher score indicates better vigor.

SEL IND=SELECTION INDEX. The selection index gives a single measure ofthe hybrid's worth based on information for up to five traits. A cornbreeder may utilize his or her own set of traits for the selectionindex. One of the traits that is almost always included is yield. Theselection index data presented in the tables represent the mean valueaveraged across testing stations.

STA GRN=STAY GREEN. Stay green is the measure of plant health near thetime of black layer formation (physiological maturity). A high scoreindicates better late-season plant health.

STK CNT=NUMBER OF PLANTS. This is the final stand or number of plantsper plot.

STK LDG=STALK LODGING. This is the percentage of plants that did notstalk lodge (stalk breakage) as measured by either natural lodging orpushing the stalks and determining the percentage of plants that breakbelow the ear.

TAS BLS=TASSEL BLAST. A 1 to 9 visual rating was used to measure thedegree of blasting (necrosis due to heat stress) of the tassel at timeof flowering. A 1 would indicate a very high level of blasting at timeof flowering, while a 9 would have no tassel blasting.

TAS SZ=TASSEL SIZE. A 1 to 9 visual rating was used to indicate therelative size of the tassel. The higher the rating the larger thetassel.

TAS WT=TASSEL WEIGHT. This is the average weight of a tassel (grams)just prior to pollen shed.

TEX EAR=EAR TEXTURE. A 1 to 9 visual rating was used to indicate therelative hardness (smoothness of crown) of mature grain. A 1 would bevery soft (extreme dent) while a 9 would be very hard (flinty or verysmooth crown).

TILLER=TILLERS. A count of the number of tillers per plot that couldpossibly shed pollen was taken. Data is given as percentage of tillers:number of tillers per plot divided by number of plants per plot.

TST WT=TEST WEIGHT (UNADJUSTED). The measure of the weight of the grainin pounds for a given volume (bushel).

TST WTA=TEST WEIGHT ADJUSTED. The measure of the weight of the grain inpounds for a given volume (bushel) adjusted for percent moisture.

YLD=YIELD. It is the same as BU ACR ABS.

YLD SC=YIELD SCORE. A 1 to 9 visual rating was used to give a relativerating for yield based on plot ear piles. The higher the rating thegreater visual yield appearance.

MDM CPX=Maize Dwarf Mosaic Complex (MDMV=Maize Dwarf Mosaic Virus &MCDV=Maize Chlorotic Dwarf Virus): Visual rating (1-9 score) where a "1"is very susceptible and a "9" is very resistant.

SLF BLT=Southern Leaf Blight (Bipolaris maydis, Helminthosporiummaydis): Visual rating (1-9 score) where a "1" is very susceptible and a"9" is very resistant.

NLF BLT=Northern Leaf Blight (Exserohilum turcicum, H. turcicum): Visualrating (1-9 score) where a "1" is very susceptible and a "9" is veryresistant.

COM RST=Common Rust (Puccinia sorghi): Visual rating (1-9 score) where a"1" is very susceptible and a "9" is very resistant.

GLF SPT=Gray Leaf Spot (Cercospora zeae-maydis): Visual rating (1-9score) where a "1" is very susceptible and a "9" is very resistant.

STW WLT=Stewart's Wilt (Erwinia stewartii): Visual rating (1-9 score)where a "1" is very susceptible and a "9" is very resistant.

HD SMT=Head Smut (Sphacelotheca reiliana): Percentage of plants that didnot have infection.

EAR MLD=General Ear Mold: Visual rating (1-9 score) where a "1" is verysusceptible and a "9" is very resistant. This is based on overall ratingfor ear mold of mature ears without determining specific mold organism,and may not be predictive for a specific ear mold.

ECB DPE=Dropped ears due to European Corn Borer (Ostrinia nubilalis):Percentage of plants that did not drop ears under second brood cornborer infestation.

ECB 2SC=European Corn Borer Second Brood (Ostrinia nubilalis): Visualrating (1-9 score) of post flowering damage due to infestation byEuropean Corn Borer. A "1"is very susceptible and a "9" is veryresistant.

ECB 1LF=European Corn Borer First Brood (Ostrinia nubilalis): Visualrating (1-9 score) of pre-flowering leaf feeding by European Corn Borer.A "1" is very susceptible and a "9" is very resistant.

DETAILED DESCRIPTION OF THE INVENTION

Inbred corn line PHRD6 is a yellow, dent corn inbred that provides anacceptable male parental line in crosses for producing first generationF1 corn hybrids. The inbred produces a white cob.

PHRD6 produces hybrids which are early flowering, high yielding and haveexcellent drydown. The inbred is unusual in that it has characteristicswhich allow it to be adapted for special usage in both the EasternUnited States and the Plains states, as well as in the North Centralpart of the United States where hybrids of similar maturities arenormally grown. These traits, which make it an exceptional line for usein the Plains states, include: good yield, early flowering, Goss's Wiltresistance, Head Smut resistance, brittlestalk resistance and droughttolerance. The traits which make it an exceptional line for use in theEastern United States and Canada include: good yield, early flowering,Head Smut resistance, high test weight, good grain quality and aboveaverage Gibberella ear mold tolerance. The grain quality and test weightthat PHRD6 conveys to its hybrids make PHRD6's hybrids exceptional foruse by poultry farmers and farmers who harvest high moisture corn. Theearly flowering, high yield and excellent drydown characteristics helpmake the line especially well adapted to the Northern parts of theUnited States corn belt where the growing season is limited by the daysbetween killing frosts and the number of heat units available in thegrowing season.

In addition, PHRD6 flowers early, has a very large tassel and sheds alarge amount of pollen. PHRD6 has good staygreen, test weight and goodbrittle stalk resistance.

The inbred has shown uniformity and stability within the limits ofenvironmental influence for all the traits as described in the VarietyDescription Information (Table 1) that follows. Most of the data in theVariety Description information was collected at Johnston, Iowa. Theinbred has been self-pollinated and ear-rowed a sufficient number ofgenerations with careful attention paid to uniformity of plant type toensure homozygosity and phenotypic stability. The line has beenincreased both by hand and in isolated fields with continued observationfor uniformity. No variant traits have been observed or are expected inPHRD6.

Inbred corn line PHRD6, being substantially homozygous, can bereproduced by planting seeds of the line, growing the resulting cornplants under self-pollinating or sib-pollinating conditions withadequate isolation, and harvesting the resulting seed, using techniquesfamiliar to the agricultural arts.

                  TABLE 1                                                         ______________________________________                                        VARIETY DESCRIPTION INFORMATION                                               INBRED = PHRD6                                                                ______________________________________                                        Type: Dent  Region Best Adapted:                                                                         North East and                                                                North Central                                      A.  Maturity: Average across maturity zones.                                      Heat Unit Shed:   1260                                                        Heat Unit Silk:   1270                                                        No. Reps:         19                                                       ##STR1##                                                                     B.  Plant Characteristics:                                                        Plant height (to tassel tip):                                                                   206 cm                                                      Length of top ear internode:                                                                    14 cm                                                       Number of ears per stalk:                                                                       Single                                                      Ear height (to base of top                                                                      62 cm                                                       ear):                                                                         Number of tillers:                                                                              1-2                                                         Cytoplasm type:   Normal                                                  C.  Leaf:                                                                         Color:            (WF9) Medium Green                                          Angle from Stalk: <30 degrees                                                 Marginal Waves:   (WF9) Few                                                   Number of Leaves (mature                                                                        17                                                          plants):                                                                      Sheath Pubescence:                                                                              (W22) Light                                                 Longitudinal Creases:                                                                           (OH56A) Few                                                 Length (Ear node leaf):                                                                         69 cm                                                       Width (widest point, ear                                                                        11 cm                                                       node leaf):                                                               D.  Tassel:                                                                       Number lateral branches:                                                                        8                                                           Branch Angle from central                                                                       >45 degrees                                                 spike:                                                                        Pollen Shed:      Heavy based on Pollen Yield                                                   Test (148% of experiment                                                      means)                                                      Peduncle Length (top leaf to                                                                    26 cm                                                       basal branches):                                                              Anther Color:     Yellow                                                      Glume Color:      Green                                                   E.  Ear (Husked Ear Data Except When Stated Otherwise):                           Length:           14 cm                                                       Weight:           113 gm                                                      Mid-point Diameter:                                                                             41 mm                                                       Silk Color:       Green                                                       Husk Extension (Harvest                                                                         Long (8-10 cm beyond ear tip)                               stage):                                                                       Husk Leaf:        Short (<8 cm)                                               Taper of Ear:     Extreme                                                     Position of Shank (dry                                                                          Upright                                                     husks):                                                                       Kernel Rows:      Straight, Distinct Number =                                                   14                                                          Husk Color (fresh):                                                                             Light Green                                                 Husk Color (dry): Buff                                                        Shank Length:     10 cm                                                       Shank (No. of internodes):                                                                      8                                                       F.  Kernel (Dried):                                                               Size (from ear mid-point)                                                     Length:           11 mm                                                       Width:            7 mm                                                        Thick:            5 mm                                                        Shape Grade (% rounds):                                                                         <20 (15% medium round                                                         based on Parent Test Data)                                  Pericarp Color:   Colorless                                                   Aleurone Color:   Homozygous Yellow                                           Endosperm Color:  Yellow                                                      Endosperm Type:   Normal Starch                                               Gm Wt/100 Seeds (unsized):                                                                      25 gm                                                   G.  Cob:                                                                          Diameter at mid-point:                                                                          23 mm                                                       Strength:         Strong                                                      Color:            White                                                   H.  Diseases:                                                                     N. Leaf Blight (E. turcicum):                                                                   Resistant                                                   Common Rust (P. sorghi):                                                                        Resistant                                                   Stewart's Wilt (E. stewartii):                                                                  Susceptible                                                 Head Smut (S. reiliana):                                                                        Highly Resistant                                            Fusarium Ear Mold Resistant                                                   (F. moniliforme):                                                             Gibberella Ear Rot (G.                                                                          Resistant                                                   zeae):                                                                    I.  Insects:                                                                      European Corn Borer-1 Leaf                                                                      Intermediate                                                Damage (Preflowering):                                                    The above descriptions are based on a scale of 1-9, 1 being                   highly susceptible, 9 being highly resistant.                                     S (Susceptible):  Would generally represent a                                                   score of 1-3.                                               I (Intermediate): Would generally represent a                                                   score of 4-5.                                               R (Resistant):    Would generally represent a                                                   score of 6-7.                                               H (Highly Resistant):                                                                           Would generally represent a                                                   score of 8-9. Highly resistant                                                does not imply the inbred is                                                  immune.                                                 J.  Variety Most Closely Resembling:                                              Character    Inbred                                                           Maturity     PHK76                                                            Usage        PHK76                                                        PHK76 (PVP Certificate No. 8800036) is a Pioneer Hi-Bred                      International, Inc. proprietary inbred.                                       ______________________________________                                         *If maximum is greater than 86 degrees fahrenheit, then 86 is used and if     minimum is less than 50, then 50 is used. Heat units accumulated daily an     can not be less than 0.                                                  

D. Tassel:

Data for Items B, C, D, E, F, and G is based primarily on a maximum oftwo reps from Johnston, Iowa grown in 1992, plus description informationfrom the maintaining station.

ELECTROPHORESIS RESULTS Isozyme Genotypes for PHRD6

Isozyme data were generated for inbred corn line PHRD6 according to theprocedures described in Stuber, C. W., Wendel, J. F., Goodman, M. M.,and Smith, J. S. C., "Techniques and Scoring Procedures for Starch GelElectrophoresis of Enzymes from Maize (Zea mays L.)", Technical BulletinNo. 286, North Carolina Agricultural Research Service, North CarolinaState University, Raleigh, N.C. (1988).

The data in Table 2 compares PHRD6 with its parents, PHK76 and PHG68.

                  TABLE 2                                                         ______________________________________                                        ELECTROPHORESIS RESULTS FOR PHRD6                                             AND ITS PARENTS PHK76 AND PHG68                                                                PARENTS                                                      LOCI     PHRD6         PHK76   PHG68                                          ______________________________________                                        ACP1     4             3       4                                              ADH1     4             4       4                                              CAT3     9             9       9                                              DIA1     8             8       8                                              GOT1     4             4       4                                              GOT2     4             4       4                                              GOT3     4             4       4                                              IDH1     4             4       4                                              IDH2     6             6       6                                              MDH1     6             6       6                                              MDH2     6             6       6                                              MDH3     16            16      16                                             MDH4     12            12      12                                             MDH5     12            12      12                                             MMM      4             4       4                                              PGM1     9             9       9                                              PGM2     4             4       4                                              PGD1       3.8         2         3.8                                          PGD2     5             5       5                                              PHI1     4             5       4                                              ______________________________________                                    

EXAMPLES Inbred and Hybrid Performance of PHRD6

In the examples that follow, the traits and characteristics of inbredcorn line PHRD6 are given as a line in comparison with other inbreds andin hybrid combination. The data collected on inbred corn line PHRD6 ispresented for the key characteristics and traits.

Table 3A compares PHRD6 to PHK76. The data shows PHRD6 has lower yieldand grain harvest moisture but higher test weight than PHK76. PHRD6 is asignificantly earlier inbred than PHK76 and would be expected to belower yielding since its hybrids would be adapted to areas with shortergrowing seasons than PHK76. If the growing season is shorter, the PHRD6would have a yield advantage in that its hybrids would be more maturewhen the growing season ends. PHRD6 is a slightly shorter inbred withlower ear placement compared to PHK76. PHRD6 flowers (GDU Shed and GDUSilk) earlier than PHK76. PHRD6 has better seedling vigor and higherearly stand count compared to PHK76.

Table 3B shows PHRD6 has higher yield and grain harvest moisture thanPHW06. PHRD6 has a larger ear, is taller and has lower ear placementthan PHW06. PHRD6 has higher early stand count and flowers (GDU Shed andGDU Silk) later compared to PHW06. PHRD6 has significantly higher pollenweight and larger tassel compared to PHW06. PHRD6 has better grainappearance, is more susceptible to root lodging but has better ear moldresistance than PHW06.

Table 3C shows PHRD6 has higher yield, grain harvest moisture and testweight than PHT73. PHRD6 has larger ear and is a taller inbred withlower ear placement compared to PHT73. PHRD6 has a higher early standcount and flowers (GDU Shed and GDU Silk) later than PHT73. PHRD6 hassignificantly higher pollen weight and larger tassel than PHT73.

Table 4A compares PHRD6 and PHBA6 when both were crossed to the sameinbred. The PHRD6 hybrid has higher yield and grain harvest moisturecompared to the PHBA6 hybrid. The PHRD6 hybrid has higher early standcount and is shorter with lower ear placement than the PHBA6 hybrid.

Table 4B compares PHRD6 to PHG47 when both were crossed to the sameinbred. The PHG47 hybrid is a high yielding hybrid for its maturity andgeographic area and yet the PHRD6 hybrid has even higher yield and testweight compared to the PHG47 hybrid. The PHRD6 hybrid has better stalklodging resistance and grain appearance plus a higher early stand countthan the PHG47 hybrid.

Table 4C compares PHRD6 to PHRE1 when both were crossed to the sameinbred. The hybrids yield similarly but the PHRD6 hybrid has asignificantly higher test weight. The PHRD6 hybrid is taller with lowerear placement compared to the PHRE1 hybrid.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 compares the yield of PHRD6 and PHW06. PHRD6 has above averageyield across all environments whereas PHW06 has below average yieldacross all environments.

Thus, it can be seen that this inbred produces hybrids adapted to theshort growing season of the North East and North Central region and yetcan also be successfully planted in the Plains area as well. Itshybrids' yields exceed other hybrids for its maturity including the highyielding PHG47 hybrid. Further, it provides excellent brittlesnaptolerance and drought tolerance.

                                      TABLE 3A                                    __________________________________________________________________________    PAIRED INBRED COMPARISON DATA                                                 VARIETY #1 - PHRD6                                                            VARIETY #2 - PHK76                                                            __________________________________________________________________________                BU   BU  YLD     EAR BAR PLT  EAR SDG                                     VAR ACR  ACR SC. MST SZ  PLT HT   HT  VGR                             DEPT    #   ABS  % MN                                                                              ABS ABS ABS ABS ABS  ABS ABS                             __________________________________________________________________________    TOTAL SUM                                                                             1   75.6 109 5.5 15.7                                                                              6.0 90.4                                                                              76.2 27.0                                                                              4.7                                     2   80.9 118 6.0 16.7                                                                              7.5 95.1                                                                              78.7 29.3                                                                              3.7                                     LOCS                                                                              3    3   2   5   2   14  11   11  13                                      REPS                                                                              18   18  2   20  2   29  17   20  20                                      DIFF                                                                              5.4  8   0.5 1.0 1.5 4.8 2.4  2.2 1.0                                     PROB                                                                              .405 .419                                                                              .500                                                                              .205                                                                              .205                                                                              .107                                                                              .307 .333                                                                              .053*                           __________________________________________________________________________                EST  TIL GDU   GDU   POL POL POL                                                                              TAS                                                                              TAS                                    VAR CNT  LER SHD   SLK   WT  WT  SC BLS                                                                              SZ                             DEPT    #   ABS  ABS ABS   ABS   ABS % MN                                                                              ABS                                                                              ABS                                                                              ABS                            __________________________________________________________________________    TOTAL SUM                                                                             1   34.6 1.3 1214  1222  161.6                                                                             145 6.8                                                                              9.0                                                                              7.2                                    2   28.3 5.8 1279  1306  201.9                                                                             183 6.3                                                                              9.0                                                                              5.3                                    LOCS                                                                              25   14  16    15    3   3   5  2  6                                      REPS                                                                              64   29  21    18    6   6   8  4  6                                      DIFF                                                                              6.3  4.5 66    83    40.3                                                                              38  0.5                                                                              0.0                                                                              1.8                                    PROB                                                                              .000#                                                                              .195                                                                              .000# .000# .204                                                                              .255                                                                              .266                                                                             1.00                                                                             .048+                          __________________________________________________________________________                TEX TST SCT STA  STK EAR NLF                                                                              STW ECB ECB                                   VAR EAR WT  GRN GRN  LDG MLD BLT                                                                              WLT 1LF 2SC                           DEPT    #   ABS ABS ABS ABS  ABS ABS ABS                                                                              ABS ABS ABS                           __________________________________________________________________________    TOTAL SUM                                                                             1   8.0 61.9                                                                              8.5 3.9  82.9                                                                              9.0 5.0                                                                              3.0 5.6 7.0                                   2   8.5 59.8                                                                              8.0 5.4  84.6                                                                              9.0 7.5                                                                              5.0 6.8 7.0                                   LOCS                                                                              2   3   2   6    4   2   2  1   5   1                                     REPS                                                                              2   17  2   14   11  2   2  1   5   1                                     DIFF                                                                              0.5 2.0 0.5 1.5  1.7 0.0 2.5                                                                              2.0 1.2 0.0                                   PROB                                                                              .500                                                                              .082*                                                                             .500                                                                              .008#                                                                              .844                                                                              1.00                                                                              .500   .235                              __________________________________________________________________________     * = 10% SIG                                                                   + = 5% SIG                                                                    # = 1% SIG                                                               

                                      TABLE 3B                                    __________________________________________________________________________    PAIRED INBRED COMPARISON DATA                                                 VARIETY #1 - PHRD6                                                            VARIETY #2 - PHW06                                                            __________________________________________________________________________                 BU   BU   YLD       EAR  BAR  PLT  EAR  SDG  EST                         VAR  ACR  ACR  SC   MST  SZ   PLT  HT   HT   VGR  CNT                 DEPT    #    ABS  % MN ABS  ABS  ABS  ABS  ABS  ABS  ABS  ABS                 __________________________________________________________________________    TOTAL SUM                                                                             1    67.4 112  6.4  20.4 5.7  89.6 74.7 26.2 5.2  44.2                        2    37.3 61   4.4  16.5 3.0  94.5 68.5 24.0 5.8  40.8                        LOCS 9    9    5    11   3    14   17   17   10   29                          REPS 20   20   5    22   3    16   23   23   11   64                          DIFF 30.0 52   2.0  3.9  2.7  4.9  6.2  2.2  0.6  3.4                         PROB .000#                                                                              .000#                                                                              .003#                                                                              .000#                                                                              .015+                                                                              .185 .000#                                                                              .035+                                                                              .415 .000#               __________________________________________________________________________                 DRP  TIL  GDU   GDU   POL  POL  POL  TAS TAS  TEX                        VAR  EAR  LER  SHD   SLK   WT   WT   SC   BLS SZ   EAR                DEPT    #    ABS  ABS  ABS   ABS   ABS  % MN ABS  ABS ABS  ABS                __________________________________________________________________________    TOTAL SUM                                                                             1    99.8 1.0  1217  1216  171.8                                                                              148  6.1  9.0 6.6  7.3                        2    99.8 4.4  1126  1164  86.9 72   5.2  8.0 4.5  6.5                        LOCS 6    22   23    20    6    6    13   4   8    4                          REPS 14   34   33    27    12   12   20   7   8    4                          DIFF 0.0  3.4  91    52    84.9 76   0.8  1.0 2.1  0.8                        PROB .901 .056*                                                                              .000# .000# .000#                                                                              .002#                                                                              .109 .391                                                                              .001#                                                                              .319               __________________________________________________________________________                  TST  GRN   SCT  STA  STK  RT   EAR  NLF ECB  ECB                         VAR  WT   APP   GRN  GRN  LDG  LDG  MLD  BLT 1LF  2SC                DEPT     #    ABS  ABS   ABS  ABS  ABS  ABS  ABS  ABS ABS  ABS                __________________________________________________________________________    TOTAL SUM                                                                              1    59.0 7.2   8.4  5.8  93.0 60.6 9.0  3.0 5.3  6.5                         2    59.5 5.6   7.4  1.3  97.9 99.3 7.8  2.0 6.4  5.8                         LOCS 9    5     5    3    6    4    5    1   4    2                           REPS 20   12    5    4    14   10   5    1   6    3                           DIFF 0.5  1.6   1.0  4.5  4.9  38.7 1.2  1.0 1.1  0.8                         PROB .369 .020+ .034+                                                                              .107 .220 .067*                                                                              .033+    .080*                                                                              .205               __________________________________________________________________________     * = 10% SIG                                                                   + = 5% SIG                                                                    # = 1% SIG                                                               

                                      TABLE 3C                                    __________________________________________________________________________    PAIRED INBRED COMPARISON DATA                                                 VARIETY #1 - PHRD6                                                            VARIETY #2 - PHT73                                                            __________________________________________________________________________                 BU   BU    YLD      EAR BAR  PLT   EAR                                   VAR  ACR  ACR   SC  MST  SZ  PLT  HT    HT                            DEPT    #    ABS  % MN  ABS ABS  ABS ABS  ABS   ABS                           __________________________________________________________________________    TOTAL SUM                                                                             1    75.6 109   5.8 18.0 5.7 86.8 77.1  25.6                                  2    24.3 34    4.8 14.8 4.3 84.8 65.4  16.9                                  LOCS 3    3     4   3    3   7    11    11                                    REPS 6    6     4   6    3   10   13    13                                    DIFF 51.2 76    1.0 3.2  1.3 2.0  11.8  8.7                                   PROB .038+                                                                              .055* .308                                                                              .057*                                                                              .270                                                                              .804 .000# .000#                         __________________________________________________________________________                SDG EST  TIL  GDU   GDU   POL  POL  POL                                   VAR VGR CNT  LER  SHD   SLK   WT   WT   SC                            DEPT    #   ABS ABS  ABS  ABS   ABS   ABS  % MN ABS                           __________________________________________________________________________    TOTAL SUM                                                                             1   4.6 43.4 1.5  1211  1220  171.8                                                                              148  5.8                                   2   5.6 41.1 12.0 1094  1124  76.2 63   4.5                                   LOCS                                                                              9   22   18   18    17    6    6    12                                    REPS                                                                              12  53   28   26    24    12   12   19                                    DIFF                                                                              1.0 2.3  10.5 117   96    95.6 85   1.3                                   PROB                                                                              .187                                                                              .000#                                                                              .005#                                                                              .000# .000# .002#                                                                              .002#                                                                              .011+                         __________________________________________________________________________                 TAS TAS TEX TST  SCT STA  STK  EAR  ECB                                  VAR  BLS SZ  EAR WT   GRN GRN  LDG  MLD  1LF                          DEPT    #    ABS ABS ABS ABS  ABS ABS  ABS  ABS  ABS                          __________________________________________________________________________    TOTAL SUM                                                                             1    9.0 6.5 7.3 61.9 8.3 3.4  89.7 9.0  5.0                                  2    9.0 4.5 5.3 57.3 8.0 1.0  94.7 5.5  4.0                                  LOCS 4   6   4   3    4   4    3    4    1                                    REPS 7   6   4   6    4   7    6    4    1                                    DIFF 0.0 2.0 2.0 4.6  0.3 2.4  5.0  3.5  1.0                                  PROB 1.00                                                                              .001#                                                                             .116                                                                              .014+                                                                              .391                                                                              .005#                                                                              .517 .069*                             __________________________________________________________________________     * = 10% SIG                                                                   + = 5% SIG                                                                    # = 1% SIG                                                               

                                      TABLE 4A                                    __________________________________________________________________________    VARIETY #1 - PHRD6 HYBRID                                                     VARIETY #2 - PHBA6 HYBRID                                                     __________________________________________________________________________                        BU   BU        STK RT  STA TST                                    VAR     PRM ACR  ACR  MST  LDG LDG GRN WTA                            DEPT    #   PRM SHD ABS  % MN % MN % MN                                                                              % MN                                                                              % MN                                                                              % MN                           __________________________________________________________________________    TOTAL SUM                                                                             1   98  97  143.7                                                                              107  98   101 91  89  99                                     2   97  98  132.0                                                                              98   95   102 97  83  99                                     LOCS                                                                              13  8   41   41   42   37  14  8   38                                     REPS                                                                              13  8   60   60   61   53  22  8   55                                     DIFF                                                                              0   1   11.7 9    3    1   6   6   0                                      PROB                                                                              .413                                                                              .350                                                                              .000#                                                                              .000#                                                                              .002#                                                                              .149                                                                              .150                                                                              .580                                                                              .540                           __________________________________________________________________________                GRN  SDG  EST  STK PLT  EAR  DRP  GDU                                     VAR APP  VGR  CNT  CNT HT   HT   EAR  SHD                             DEPT    #   % MN % MN % MN % MN                                                                              % MN % MN % MN % MN                            __________________________________________________________________________    TOTAL SUM                                                                             1   103  90   102  100 101  97   100  100                                     2   97   93   97   99  105  104  100  100                                     LOCS                                                                              31   24   29   50  18   18   20   14                                      REPS                                                                              41   29   35   72  23   23   27   19                                      DIFF                                                                              6    3    5    1   5    7    0    0                                       PROB                                                                              .108 .532 .005#                                                                              .110                                                                              .002#                                                                              .023+                                                                              .330 .517                            __________________________________________________________________________     * = 10% SIG                                                                   + = 5% SIG                                                                    # = 1% SIG                                                               

                                      TABLE 4B                                    __________________________________________________________________________    VARIETY #1 - PHRD6 HYBRID                                                     VARIETY #2 - PHG47 HYBRID                                                     __________________________________________________________________________                        BU   BU       STK  RT  STA TST                                    VAR     PRM ACR  ACR  MST LDG  LDG GRN WTA                            DEPT    #   PRM SHD ABS  % MN % MN                                                                              % MN % MN                                                                              % MN                                                                              % MN                           __________________________________________________________________________    TOTAL SUM                                                                             1   98  96  147.7                                                                              107  100 101  91  98  99                                     2   98  98  141.9                                                                              102  100 97   93  96  98                                     LOCS                                                                              19  13  61   61   62  56   15  13  58                                     REPS                                                                              19  13  98   98   99  90   24  19  93                                     DIFF                                                                              0   1   5.9  4    0   5    2   2   1                                      PROB                                                                              .348                                                                              .067*                                                                             .006#                                                                              .006#                                                                              .857                                                                              .008#                                                                              .734                                                                              .724                                                                              .000#                          __________________________________________________________________________                GRN  SDG EST  STK PLT  EAR DRP GDU  BRT                                   VAR APP  VGR CNT  CNT HT   HT  EAR SHD  STK                           DEPT    #   % MN % MN                                                                              % MN % MN                                                                              % MN % MN                                                                              % MN                                                                              % MN ABS                           __________________________________________________________________________    TOTAL SUM                                                                             1   104  93  102  100 101  98  100 99   97.2                                  2   94   89  96   100 100  96  100 100  96.8                                  LOCS                                                                              46   34  41   69  27   27  31  21   52                                    REPS                                                                              70   48  59   109 40   40  48  32   56                                    DIFF                                                                              10   4   6    0   1    2   0   2    0.4                                   PROB                                                                              .002#                                                                              .153                                                                              .000#                                                                              .601                                                                              .385 .228                                                                              .297                                                                              .010+                                                                              .518                          __________________________________________________________________________     * = 10% SIG                                                                   + = 5% SIG                                                                    # = 1% SIG                                                               

                                      TABLE 4C                                    __________________________________________________________________________    VARIETY #1 - PHRD6 HYBRID                                                     VARIETY #2 - PHRE1 HYBRID                                                     __________________________________________________________________________                         BU  BU       STK RT   STA TST                                    VAR     PRM  ACR ACR  MST LDG LDG  GRN WTA                            DEPT    #   PRM SHD  ABS % MN % MN                                                                              % MN                                                                              % MN % MN                                                                              % MN                           __________________________________________________________________________    TOTAL SUM                                                                             1   98  97   140.2                                                                             106  100 101 91   89  99                                     2   98  96   141.8                                                                             108  98  101 106  73  98                                     LOCS                                                                              14  9    46  46   48  41  14   8   44                                     REPS                                                                              14  9    66  66   68  58  22   8   62                                     DIFF                                                                              0   1    1.6 2    1   0   15   16  1                                      PROB                                                                              .355                                                                              .197 .490                                                                              .294 .341                                                                              .875                                                                              .025+                                                                              .481                                                                              .000#                          __________________________________________________________________________                GRN SDG  EST STK PLT  EAR  DRP GDU BRT                                    VAR APP VGR  CNT CNT HT   HT   EAR SHD STK                            DEPT    #   % MN                                                                              % MN % MN                                                                              % MN                                                                              % MN % MN % MN                                                                              % MN                                                                              ABS                            __________________________________________________________________________    TOTAL SUM                                                                             1   104 92   102 100 102  99   100 100 97.1                                   2   102 103  102 101 99   107  100 99  92.5                                   LOCS                                                                              34  28   31  55  21   21   21  15  50                                     REPS                                                                              44  34   38  78  27   27   28  21  54                                     DIFF                                                                              2   11   0   1   3    8    0   1   4.6                                    PROB                                                                              .617                                                                              .007#                                                                              .985                                                                              .420                                                                              .015+                                                                              .019+                                                                              .594                                                                              .227                                                                              .000#                          __________________________________________________________________________     * = 10% SIG                                                                   + = 5% SIG                                                                    # = 1% SIG                                                               

INDUSTRIAL APPLICABILITY

The foregoing is set forth by way of example and is not intended tolimit the scope of the invention.

This invention also is directed to methods for producing a corn plant bycrossing a first parent corn plant with a second parent corn plantwherein the first or second parent corn plant is an inbred corn plantfrom the line PHRD6. Further, both first and second parent corn plantscan come from the inbred corn line PHRD6. Thus, any such methods usingthe inbred corn line PHRD6 are part of this invention: selfing,backcrosses, hybrid production, crosses to populations, and the like. Italso would include more unconventional methods of combining the inbredwith another such as using various culturing techniques known to thoseskilled in the art. All plants produced using inbred corn line PHRD6 asa parent are within the scope of this invention. Advantageously, theinbred corn line is used in crosses with other, different, corn inbredsto produce first generation (F₁) corn hybrid seeds and plants withsuperior characteristics.

Corn plants (Zea mays L.) can be bred by both self-pollination andcross-pollination techniques. Corn has male flowers, located on thetassel, and female flowers, located on the ear, on the same plant.Natural pollination occurs in corn when wind blows pollen from thetassels to the silks that protrude from the tops of the incipient ears.Backcrossing can be used to transfer monogenic traits from on line toanother. This can be accomplished for example by first crossing asuperior inbred (A) (recurrent parent) to a donor inbred (non-recurrentparent), which carries the appropriate gene(s) for the trait inquestion. The progeny of this cross is then mated back to the superiorrecurrent parent (A) followed by selection in the resultant progeny forthe desired trait to be transferred from the non-recurrent parent. Afterfive or more backcross generations with selection for the desired trait,the progeny will be heterozygous for loci controlling the characteristicbeing transferred, but will be like the superior parent for most oralmost all other genes. The last backcross generation would be selfed togive pure breeding progeny for the gene(s) being transferred.

Hybrid corn seed is produced by planting male and female parental linesin sufficient proximity to permit pollination of the female line by themale line ("pollinating proximity"). To assure genetic uniformity andavoid self-pollination, steps are taken to prevent pollen formation bythe plants of the parental line chosen to serve as the female. This ismost commonly done by manual detasseling. Alternate strips of theparental lines of corn are planted in a field, and the pollen-bearingtassels are physically removed from the female plants, either by hand orby machine. Providing that there is sufficient isolation from othersources of corn pollen, the ears of the female plants will be fertilizedonly from pollen from the male plants, and the resulting seed istherefore hybrid and will form hybrid plants. In a single-cross hybrid,both parents are inbred lines. In a double-cross hybrid, both parentsare the F₁ offspring of a cross of two inbred lines. In a three-waycross, one of the parents is an inbred line and the other parent is anF₁ hybrid. Each cross is made in the manner described herein.

Unfortunately, the manual detasseling process is not entirely reliable.Occasionally a female plant will be blown over by a storm and escapedetasseling. Or, a detasseler will not completely remove the tassel ofthe plant. In either event, the female plant will successfully shedpollen and some female plants will be self-pollinated. This will resultin seed of the female inbred being harvested along with the hybrid seedwhich is normally produced.

Alternatively, the female inbred can be mechanically detasseled.Mechanical detasseling is approximately as reliable as manualdetasseling, but is faster and less costly. However, most detasselingmachines produce more damage to the plants than manual detasseling.

The laborious detasseling process can be avoided by using cytoplasmicmale-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile (donot form pollen) as a result of cytoplasmic factors resulting from thecytoplasmic, as distinguished from the nuclear, genome. Thus, thischaracteristic is inherited exclusively through the female parent, sincethe female parent provides the cytoplasm of the fertilized seed. CMSplants are fertilized with pollen from another inbred that is notmale-sterile. Pollen from the male parent may or may not contributegenes that make the hybrid plants male-fertile. Usually seed fromdetasseled normal maize and CMS-produced seed of the same hybrid must beblended to insure that adequate pollen loads are available forfertilization when the hybrid plants are grown.

There can be other drawbacks to CMS. One is an historically observedassociation of a specific variant of CMS with susceptibility to certaincrop diseases. This problem has led to widespread abandonment of use ofthat CMS variant in producing hybrid maize. In addition, CMS sometimeshas a negative association with agronomic performance, particularly inthe areas of stalk quality, early seedling vigor, and yield. Finally,CMS exhibits on occasion the potential for breakdown of sterility incertain environments, rendering CMS lines unreliable for hybrid seedproduction.

Another form of sterility, genic male sterility, is disclosed in U.S.Pat. Nos. 4,654,465 and 4,727,219 to Brar et al. However, this form ofgenetic male sterility requires maintenance of multiple mutant genes atseparate locations within the genome and requires a complex markersystem to track the genes and make use of the system convenient.

Another form of male sterility is imparted in a manner by whichexpression of a transgene produces a "pollen-toxic" compound whichblocks pollen formation in some manner.

Still another form of genetic male sterility uses an inducible promoterto regulate expression of a gene which is known to be critical inmicrosporogenesis, i.e., the production of pollen. The selected gene iscloned, its native promoter removed, and the modified gene is insertedinto an expression sequence with an inducible promoter responsive toexternal control. Preferably, the promoter is one which responds toapplication of a specific non-phytotoxic chemical to the plant.

Using transformation and gene substitution, the "critical" gene isdeleted from the genome of the plant and replaced by thegenetically-engineered gene incorporated into the expression sequencewith the inducible promoter. In this method, the inducible promoter isused to induce fertility, not sterility. The selected gene's promotersequences are removed so that the gene is not transcribed and the plantis male sterile. When it is desired to increase the male-sterile plant,male fertility is restored by inducing expression of the critical genewith a specific non-phytotoxic chemical. Any of the foregoing methodsand combinations thereof can be used to prevent pollen formation by thefemale parent of the hybrid.

As used herein, the term plant includes plant cells, plant protoplasts,plant cell tissue cultures from which corn plants can be regenerated,plant calli, plant clumps, and plant cells that are intact in plants orparts of plants, such as embryos, pollen, flowers, kernels, ears, cobs,leaves, husks, stalks, roots, root tips, anthers, silk and the like.

Duncan, Williams, zehr, and Widholm, Planta, (1985) 165:322-332 reflectsthat 97% of the plants cultured which produced callus were capable ofplant regeneration. Subsequent experiments with both inbreds and hybridsproduced 91% regenerable callus which produced plants. In a furtherstudy in 1988, Songstad, Duncan & Widholm in Plant Cell Reports (1988),7:262-265 reports several media additions which enhance regenerabilityof callus of two inbred lines. Other published reports also indicatedthat "nontraditional" tissues are capable of producing somaticembryogenesis and plant regeneration. K. P. Rao, et al., Maize GeneticsCooperation Newsletter, 60:64-65 (1986), refers to somatic embryogenesisfrom glume callus cultures and B. V. Conger, et al., Plant Cell Reports,6:345-347 (1987) indicates somatic embryogenesis from the tissuecultures of maize leaf segments. Thus, it is clear from the literaturethat the state of the art is such that these methods of obtaining plantsare "conventional" in the sense that they are routinely used and have avery high rate of success. It should also be clear that the term"regenerable cells" as used in the claims should be construed broadly toinclude any of the foregoing examples of regenerable cells, when theyhave the genotype of PHRD6.

Tissue culture of corn is described in European Patent Application,publication 160,390, incorporated herein by reference. Corn tissueculture procedures are also described in Green and Rhodes, "PlantRegeneration in Tissue Culture of Maize," Maize for Biological Research(Plant Molecular Biology Association, Charlottesville, Va. 1982, at367-372) and in Duncan, et al., "The Production of Callus Capable ofPlant Regeneration from Immature Embryos of Numerous Zea MaysGenotypes,"165 Planta 322-332 (1985). Thus, another aspect of thisinvention is to provide cells which upon growth and differentiationproduce corn plants having the genotype of the inbred line PHRD6. Suchplants, after self-pollination, will yield plants having thephysiological and morphological characteristics of PHRD6.

Corn is used as human food, livestock feed, and as raw material inindustry. The food uses of corn, in addition to human consumption ofcorn kernels, include both products of dry- and wet-milling industries.The principal products of corn dry milling are grits, meal and flour.The corn wet-milling industry can provide corn starch, corn syrups, anddextrose for food use. Corn oil is recovered from corn germ, which is aby-product of both dry- and wet-milling industries.

Corn, including both grain and non-grain portions of the plant, is alsoused extensively as livestock feed, primarily for beef cattle, dairycattle, hogs, and poultry.

Industrial uses of corn are mainly from corn starch in the wet-millingindustry and corn flour in the dry-milling industry. The industrialapplications of corn starch and flour are based on functionalproperties, such as viscosity, film formation, adhesive properties, andability to suspend particles. The corn starch and flour have applicationin the paper and textile industries. Other industrial uses includeapplications in adhesives, building materials, foundry binders, laundrystarches, explosives, oil-well muds, and other mining applications.

Plant parts other than the grain of corn are also used in industry.Stalks and husks are made into paper and wallboard and cobs are used forfuel and to make charcoal.

The seed of inbred corn line PHRD6, the plant produced from the inbredseed, the hybrid corn plant produced from the crossing of the inbred,hybrid seed, and various parts of the hybrid corn plant can be utilizedfor human food, livestock feed, and as a raw material in industry.

Although the foregoing invention has been described in some detail byway of illustration and example for the purposes of clarity andunderstanding, it will be obvious that certain changes and modificationsmay be practiced within the scope of the invention, as limited only bythe scope of the appended claims. DEPOSITS

Applicant has made a deposit of at least 2500 seeds of Inbred Corn LinePHRD6 with the American Type Culture Collection (ATCC), Rockville, Md.20852 USA, ATCC Deposit No. 97232. The seeds deposited with the ATCC onJuly 25, 1995 were taken from the deposit maintained by Pioneer Hi-BredInternational, Inc., 700 Capital Square, 400 Locust Street, Des Moines,Iowa 50309-2340 since prior to the filing date of this application. Thisdeposit of the Inbred Corn Line PHRD6 will be maintained in the ATCCdepository, which is a public depository, for a period of 30 years, or 5years after the most recent request, or for the enforceable life of thepatent, whichever is longer, and will be replaced if it becomesnonviable during that period. Additionally, Applicant has satisfied allthe requirements of 37 C.F.R. §§1.801-1.809, including providing anindication of the viability of the sample. Applicant imposes norestrictions on the availability of the deposited material from theATCC; however, Applicant has no authority to waive any restrictionsimposed by law on the transfer of biological material or itstransportation in commerce. Applicant does not waive any infringement ofits rights granted under this patent or under the Plant VarietyProtection Act (7 USC 2321 et seq.). PHRD6 is a U.S. Protected Varietyunder Plant Variety Protection Certificate No. 9400096.

What is claimed is:
 1. Inbred corn seed designated PHRD6 and having ATCCAccession No.
 97232. 2. A corn plant and its parts produced by the seedof claim
 1. 3. A tissue culture of regenerable cells of a plant of theinbred corn line PHRD6 wherein the tissue regenerates plants having allof the physiological and morphological characteristics of PHRD6 andhaving ATCC Accession No.
 97232. 4. A tissue culture according to claim3, the tissue culture selected from the group consisting of leaves,pollen, embryos, roots, root tips, anthers, silk, flowers, kernels,ears, cobs, husks and stalks, and cells and protoplasts thereof.
 5. Acorn plant regenerated from a tissue culture of a plant of inbred cornline PHRD6 and having all of the physiological and morphologicalcharacteristics of PHRD6 having ATCC Accession No.
 97232. 6. A processto producing a hybrid corn seed which gives rise to a hybrid corn planthaving alleles which, when expressed, contribute to hybrids whichexhibit the traits of Goss's Wilt resistance and drought resistance,comprising the steps of:(a) planting, in pollinating proximity, seeds oftwo parental lines, one of the parental lines being PHRD6 having ATCCAccession No. 97232, and the other parental line having a genotypedifferent from PHRD6; (b) cultivating corn plants resulting from saidplanting; (c) preventing pollen formation by the plants of one of theparental lines; (d) allowing natural cross pollinating to occur betweensaid parental lines; and (e) harvesting seeds produced by the plantswhich do not form pollen.
 7. Hybrid seed produced by:(a) planting, inpollinating proximity, seeds of two parental lines, one of the parentallines being PHRD6 having ATCC Accession No. 97232, and the otherparental line having a genotype different from PHRD6; (b) cultivatingcorn plants resulting from said planting; (c) preventing pollenformation by the plants of one of the parental lines; (d) allowingnatural cross pollinating to occur between said parental lines; and (e)harvesting seeds produced by the plants which do not form pollen. 8.Hybrid plants and their parts grown from the hybrid seed of claim
 7. 9.A tissue culture of the regenerable cells of the corn plant generatedfrom seed produced by crossing plants of inbred corn seed designatedPHRD6 and having ATCC Accession No. 97232 and plants of a parental linehaving a genotype different from PHRD6.